(1)
Pediatric Cardiology, Policlinico S.Orsola-Malpighi, Bologna, Italy
The value of electrocardiography for diagnosing congenital heart disease has decreased considerably since the introduction of fetal ultrasound as routine antenatal screening. In the past, brilliant cardiologists used to deduce the diagnosis of tetralogy of Fallot and the relative degree of oxygen desaturation by judging the S wave in lead V6. Nowadays, an accomplished gynecologist, who suddenly has lots of ultrasound equipment and no ECG experience, can grapple quite successfully with a cardiologic diagnosis. So, univentricular hearts and complex cardiac defects are now expected to be known before the ECG is performed. Nevertheless, some conditions left undetected by antenatal screening come to light in early infancy or even later in life, following a symptomatic or random ECG recording. Right ventricular hypertrophy (RVH) beyond the expected prevalence for the age, “adult” conduction intervals, and abnormal axis deviations could all suggest an underlying CHD (Tables 1.1, 3.43.4, 18.1, 18.2, and 18.3): left axis deviation of at least −30° is suggestive of atrioventricular canal (AVC) in a “rosy pink” newborn or toddler—which is certain in trisomy 21—or of tricuspid atresia (TA) in a cyanotic baby [1]. The ECG is quite informative in the case of complex cardiac defects and right ventricular overload, while it is much less sensitive in detecting left ventricular overload. Surprisingly, the ECG could be perfect in the transposition of the great arteries (TGA)—a CHD with an absolute ductus dependency—while an asymptomatic CCTGA may leave a number of signs on the ECG even in the neonatal period: the former has a clear clinical presentation with no need of an ECG; the latter could occasionally be encountered in an ECG recording performed due to detection of a “not-quite-innocent” heart murmur or bradycardia. Post-tricuspid shunts , such as ventricular septal defect (VSD) and patent ductus arteriosus (PDA), initially cause left ventricular overload, and, if untreated, can eventually lead to Eisenmenger syndrome with predominant right ventricular hypertrophy. Ebstein anomaly , CCTGV, and isomerism-associated arrhythmias are related to specific cardiac conduction system anomalies. Children who undergo congenital heart treatment procedures are at increased risk of various hyper- and hypokinetic postoperative “incisional” arrhythmias, e.g., atrial reentry or atypical flutter (atrial septal defect, Mustard/Senning correction for the transposition of the great vessels, Fontan procedure for univentricular heart) and ventricular tachycardia (tetralogy of Fallot) [2].
Table 18.1
ECG synopsis of all CHD
Table 18.2
ECG synopsis of all CHD
Table 18.3
ECG synopsis of all CHD
A short overview of the major congenital heart defects is presented below. Some of them, in view of a certain degree of hemodynamic compensation (patent ductus, mild oxygen desaturation or shunt), could be missed inadvertently during initial clinical evaluation or encountered by chance or following symptoms in an ECG carried out as an initial cardiac diagnostic technique.
18.1 Cardiac Defects with Left-to-Right Pre-tricuspid Shunts (Atrial Septal Defects and Anomalous Pulmonary Venous Return)
In patients with small atrial septal defects (ASD) and no evidence of significant right-sided chamber dilatation, the ECG is usually normal, unless it is an ostium primum associated with a partial AV canal (left axis deviation in ostium primum vs right axis deviation in ostium secundum). With a significant left-to-right shunt, the ECG changes are proportionate to the degree of the right ventricle dilatation [3].
The rsr’ or rsR’ QRS morphology in the right precordial leads is a frequent finding, with a sluggish and polyphasic aspect of the r’ wave, secondary to right ventricle volume overload and dilatation (unfortunately rsR pattern is a not so rare finding even in young with normal heart, but the R wave amplitude counts). Starting from late childhood, an indented aspect (“crochetage”) of the R wave could be observed in the inferior leads [4]. The above electrocardiographic abnormalities are reversible, with a possible normalization of the ECG immediately after surgical closure or transcatheter occlusion with devices.
The QRS axis is usually vertical, but in the presence of significant blood shunting and elevated right ventricular systolic pressure, a rightward QRS axis and some right ventricular conduction delay (RBBB) are frequently observed. Atrial fibrillation/atypical atrial flutter and IART secondary to atrial enlargement and fibrosis may complicate the clinical picture after the second decade of life.
Adult patients with coexisting cardiovascular problems (systemic arterial hypertension, heart valve disorders, fascicular blocks) may exhibit a left QRS axis deviation, which is also characteristic of a complete or partial atrioventricular canal defect (AVC) and Holt-Oram syndrome. In major shunts, the ventricular repolarization pattern could be modified to the same extent as depolarization: as previously mentioned, negative-positive diphasism of the T wave (overshoot) in the right precordial leads is suggestive of right ventricular volume overload (“butterfly sign”). The PR interval of a classic ostium secundum ASD is normal, while its prolongation and first-degree heart block may occur in ASD ostium primum or sinus venosus type. The ECG changes in patients with anomalous pulmonary venous return, and dilated right chambers correspond to those outlined above for ASDs. On some occasions, these patients may suffer from sinus bradycardia and ectopic atrial rhythms: in fact, anomalous pulmonary venous return may be coupled with anomalous systemic venous drainage, such as a left-sided superior vena cava (LSVC) which drains into the right atrium via the coronary sinus. Both venous anomalies may cause low atrial rhythm or ectopic atrial rhythms. Sinus node dysfunction is a common postoperative complication, its frequency being inversely related to the child’s age at the time of corrective surgery. AV conduction disorders which may progress to a complete heart block are also reported in rare cases of ASD repair (e.g., sinus venosus).
18.2 Cardiac Defects with Left-to-Right Post-tricuspid Shunts (Ventricular Septal Defect and Patent Ductus Arteriosus)
As mentioned earlier for ASD, the ECG is usually normal in the case of minor ventricular septal defects (VSD) with no evidence of left chamber dilatation. With conspicuous right-to-left shunts, the ECG changes are secondary to left ventricular dilatation and hypertrophy, left atrial enlargement, and/or right ventricular pressure overload, which develop due to pulmonary arterial hypertension or infundibular pulmonary stenosis. Toddlers with a large VSD or PDA exhibit biventricular hypertrophy and equiphasic QRS complexes in the mid-precordium, known as the Katz-Wachtel phenomenon [5]. Older patients can satisfy voltage criteria for left ventricular hypertrophy. Left atrial hypertrophy or prolonged atrial depolarization and left axis deviation are often present as well. Right ventricular pressure overload is associated with pulmonary arterial hypertension or infundibular pulmonary stenosis. Most patients who have undergone repair of a subaortic ventricular septal defect develop a postoperative RBBB (much less often an LBBB which is, instead, a complication of myomectomy according to Morrow or correction of a subaortic stenosis).
18.3 Partial, Intermediate, and Complete Atrioventricular Canal
The ECG patterns ranging from left axis deviation to left anterior hemiblock reflect the underlying particular anatomy of the conduction system (the inferior displacement of the AV node and the His bundle, hypoplastic anterior fascicle of the left bundle) and the right and/or left ventricular dilatation due to significant shunting [6]. In patients with a partial (i.e., ostium primum ASD with mitral valve anomaly) or intermediate (with an associated restrictive type VSD) AV canal, apart from the left anterior fascicular block, an RBBB can be especially observed in the case of a conspicuous left-to-right shunting with right ventricular dilatation. Moreover, in patients with a complete AV canal (i.e., ostium primum ASD and a large VSD) and left-to-right shunting with biventricular dilatation (often aggravated by atrioventricular valve incompetence), a left ventricular hypertrophy or biventricular hypertrophy can complicate the above-described ECG pattern. A first-degree AV block is a frequent finding, while an advanced or complete heart block might represent a postoperative complication, especially in large inlet VSDs.
18.4 Right-Sided Obstructive Lesions (Pulmonary Stenosis, Tetralogy of Fallot, Pulmonary Atresia with VSD, and Pulmonary Atresia with Intact Ventricular Septum)
In patients with pulmonary stenosis, the ECG changes reflect the degree of right ventricular hypertrophy. The amplitude of the R wave in lead V1 has demonstrated a good correlation with the pressure gradient across the pulmonary valve [7]. Common electrocardiographic indications that are used in diagnosing right ventricular hypertrophy are a high and monophasic R wave in V1, rightward deviation of the mean QRS axis in the frontal plane, deep q waves in the inferior leads, and deep S waves in V5–V6. Upright T waves in V1 are associated with increased right ventricular pressure in children aged 7 days to 7 years of life. Right atrial enlargement, if present, represents an additional diagnostic tool for right ventricular hypertrophy. Extreme axis deviation, also known as “northwest axis,” is a characteristic finding, which is very frequent in patients with Noonan syndrome, even in the absence of significant pulmonary stenosis. There are no specific ECG changes for diagnosing tetralogy of Fallot, although the above signs of right ventricular hypertrophy are usually present. Moreover, a correlation between the degree of cyanosis and R/S voltage ratio in left precordial leads has been described: in “rosy pink” Fallot infants, the R/S voltage ratio is normal for age, while in a “cyanotic” Fallot, deep S waves can be observed in the left precordial leads with an r/S ratio < 1.
In pulmonary atresia with VSD, the ECG changes are indistinguishable from Fallot tetralogy. In the case of a large VSD, right ventricular pressures are usually equal than their systemic equivalents. On the contrary, in pulmonary atresia with intact ventricular septum, the right-sided pressures are higher than the left-sided ones, and the electric representation of the right ventricle has an inverse correlation with its degree of hypoplasia. In this case, the congenital anomaly affects the right heart as a whole, and the atretic pulmonary valve may produce no ECG changes, in view of the absent electrical predominance of the hypoplastic right ventricle which, nevertheless, is subjected to a consistent pressure overload. Right atrial enlargement, as a consequence of severe or massive tricuspid insufficiency, will guide the diagnosis.
In patients with tetralogy of Fallot who undergo corrective surgery, an RBBB is a common, almost invariable postoperative complication, usually with a quite wide QRS complex. The QRS duration may increase with time, in parallel with right ventricular dilatation secondary to pulmonary insufficiency, and represents a risk factor for ventricular arrhythmias (significant when QRS is longer than 180 ms).
18.5 Left-Sided Obstructive Lesions (Aortic Stenosis and Coarctation of the Aorta)
In young adults, the ECG sensitivity for diagnosing left ventricular hypertrophy is low, even in the presence of a severe aortic stenosis or coarctation of the aorta, while during the neonatal period and in early infancy, it is much more accurate and useful.
QRS axis deviation and prominent Q waves are some of the known ECG signs denoting left ventricular hypertrophy of at least moderate degree, while high voltage in the left leads is a more sensitive but less specific criterion [8]. In the neonatal coarctation of the aorta, the ECG signs of right ventricular overload may precede those of left overload. In terms of overload, generally the repolarization alterations are more specific and sensitive than depolarization ones.
18.6 Tricuspid Atresia
TA is the most common form of univentricular heart, actually the prototype of left univentricular heart. In the absence of a tricuspid valvular plane, the conducting system dislocates in the posterior and inferior direction (the AV node and its branches), similar to what happens in AV canal defect. A left axis deviation or a left fascicular hemiblock is thus typical ECG finding in these patients, with a quite certain diagnosis in a cyanotic infant.
18.7 Tricuspid Valve Dysplasia and Ebstein’s Anomaly
The ECG usually shows right atrial involvement with prolonged PR interval and unusual RBBB-polyphasic QRS complexes in lead V1. Right atrial involvement and PR interval prolongation are both consequences of atrial dilatation, with a subsequent atrial conduction delay. Polyphasic RBBB is due to a ventricular conduction delay in view of the “atrialization” of the upper segment of the right ventricle [9]. Negative T waves in the right precordial leads and prominent Q waves in the inferior quadrants are common. The latter is a consequence of right ventricular wall and/or septum thickening and fibrotic changes [10]. Additionally, there is an association with ventricular pre-excitation in up to 25% of cases due to the presence of accessory pathways like Kent or Mahaim, often multiple and only exceptionally left-sided [11]. These patients do not usually show a characteristic polyphasic QRS complex in V1 but a short PR interval with a delta wave. In Mahaim-type accessory pathway, a normal or prolonged PR interval with an initial slurring of the QRS complex and anterior pseudonecrosis (poor R wave progression in the anterior leads) may be observed.
18.8 Transposition of the Great Arteries (TGA)
The ECG at birth may be completely normal in the event of a simple transposition of the great vessels, without an associated VSD, pulmonary stenosis, or coarctation of the aorta. It may sometimes display right ventricular overload (as the aorta arises from the right ventricle), aggravated by systemic vascular resistance and pressure.
18.9 Congenitally Corrected Transposition of the Great Arteries (CCTGA)
Due to the mirror-imaged arrangement of the ventricles that we could simplify by calling it ventricular inversion, the activation of the interventricular septum will proceed from right to left and not, as is usually the case, from left to right. Consequently, the ECG assumes an aspect of anterior pseudonecrosis with Q waves present in the right precordial leads and absent in the lateral leads [12]. In the frontal plane left axis deviation can be frequent and positive anterior T waves are also present. In addition, since the interventricular septum activation progresses from the bottom up, there are usually deep q waves in the inferior leads as well, most evident in lead III.
A high-grade AV block is common in these patients, already present at birth or with later presentation. Estimates foresee an annual incidence of about 2% and a prevalence in adults of about 22% [13]. Arrhythmias and conduction disorders are due to the anterior dislocation of the AV node and the bundle of His, the course of the latter usually being oblong and disrupted, often running close to a VSD border (thus, a frequent postoperative AV block); the natural history of CCTGV is also characterized by a frequent histopathologic finding of a fibrotic bundle of His [14]. The morphologically right ventricle in CCTGV has a tricuspid valve that is often dysplastic even to the degree of Ebstein’s anomaly; the latter two cardiac defects could harbor accessory pathways and have a similar ECG expression both in terms of pre-excitation (accessory pathways) and post-excitation (conducting disturbances), similarly to storage disease as Fabry’s disease and PRKAG2 mutation.
18.10 Congenital Coronary Artery Anomalies
Anomalous origin of the left coronary artery from the pulmonary artery (ALCAPA) is the most common anomaly of the coronary origin. Right coronary artery anomalous origin from the pulmonary artery (ARCAPA) is a possible, but usually asymptomatic, condition in view of the minor hemodynamic significance of its blood supply compared with the left coronary artery. ALCAPA becomes symptomatic from the very first months of life, presenting on ECG with anterior and/or lateral wall necrosis with associated abnormal deep and wide q waves: as pulmonary arterial pressure drops soon after birth, the flow in the left coronary artery decreases and then reverses, resulting in the “coronary steal” phenomenon, in which a left-to-right shunt leads to abnormal left ventricular perfusion and ischemia. The extent of acquired collateral circulation between the two main coronary arteries (the right one is usually dilated!) during the critical period determines the extent of myocardial ischemia. In the rare cases of additional anatomical defects—i.e., stenotic origin of the left coronary artery—the above mechanism could be limited, causing mild symptoms and normal ECGs up to adult age. So, like ACAOS and coronary artery fistulae, ALCAPA and other coronary artery anomalies should be kept in mind for differential diagnosis in case of syncope or major arrhythmias precipitated by emotional or physical stress [15, 16]. However, ACAOS differs significantly from ALCAPA. The basic electrocardiogram in ACAOS is, in fact, always normal, as is the stress electrocardiogram. Symptoms occur on exertion, a situation in which the coronary artery that has an abnormal course between the aorta and the pulmonary artery can be crushed. The diagnosis of ACAOS is therefore eminently echocardiographic.
Fig. 18.1
(a) Ten-day-old baby girl. Sinus rhythm , P wave does not suggest overload. The QRS shows right axis deviation, standing at about 200°. The R wave in V1 is at the upper limit but it is almost monophasic, and S V6 are at the upper limit too, not frankly pathological. Left voltages are not much represented, a normal pattern for a neonate. (b) Close-up. The most interesting aspect of the repolarization is in V1: the T wave is diphasic, with prevalence of the positive terminal component. After the first week of life and up to 7 years of age, the positive T in V1 should be regarded as systolic right ventricular overload. The patient had moderate valvular pulmonary stenosis (PS)
Fig. 18.2
(a) Two-year-old male with moderate PS. (b) Similar case, 6-year-old male with moderate PS. On echo the gradient through the pulmonary valve was 70 mmHg. The right axis deviation is not impressive, 100°, as well as the R wave in V1. In both cases, the deep S wave in V6 reveals the pressure overload of the right ventricle despite the silence of the other leads. (c) Close-up
Fig. 18.3
Thirty-year-old female with severe PS. Note the qR in V1, a specific sign of severe RVH, along with ST depression
